The present disclosure generally relates to devices and methods that provide structural support to aspects of a spine, and in particular to deformable intervertebral cages and related methods that facilitate arthrodesis and/or interbody fusion and/or dynamic stabilization of a motion segment of a spine.
Spinal pathology and surgery are common practices with patients with spinal cord compression and/or nerve root compression when conservative treatments have failed. The current standard and most commonly utilized procedure in the spine is an anterior cervical discectomy and fusion (ACDF). Commonly, in ACDF one or multiple levels of the cervical spine are exposed from an anterior approach. The spine is then distracted and discectomy and decompression are performed. A bone graft or interbody implant (referred to as a “cage”) is often placed to fill the vacated disc space and to assist in maintaining disc height.
Intervertebral cages typically serve two main purposes. First, some vertebral interbody cages may act as a containment device for a bone graft. Secondly, some vertebral interbody cages may fill a vertebral body defect or an intervertebral defect and, potentially, resist axial loading of the spine. In the cervical, thoracic and lumbar regions of the spine, corpectomies, or removal of the vertebrae, is often performed, such as in cases of degenerative disease, trauma (burst fractures), tumors of the spine, and infections of the disc and vertebrae. In such cases, an intervertebral cage is usually inserted from the anterior or lateral regions of the vertebrae, though they may be applied through a posterior approach.
In typical practice, once an intervertebral cage is implanted between adjacent endplates of the spine, a spinal fixation plate is used to stabilize the spine and to foster arthrodesis. Spinal fixation plates may span a single intervertebral disc and affix to two adjacent vertebrae for a single level procedure. Multiple level applications may also be performed. Most commonly, spinal fixation plates are affixed to the vertebrae using bone fixation devices, such as bone screws.
While static bone plates may be effective at stabilizing the spine in some applications, the inventors have appreciated that they may cause graft stress shielding, graft overloading, subsidence, and/or graft failure. Another common complication associated with plate fixation in the spine, such as in the cervical spine, following anterior interbody arthrodesis is dysphagia. Dysphagia is commonly caused by irritation of the esophagus and surrounding tissue due to the implant which may extend at least partially out of the intervertebral disc space. In some embodiments, dynamic plate implants have been designed to provide load sharing during flexion/extension of the spine to minimize graft over-loading and/or promote loading through the bone graft.
All-in-one cage-plate implants may provide some of the advantages of plating including resistance to flexion-extension motion, lateral bending motion, and torsion. Cage-plate implants may also provide the advantages of cages including resistance to flexion (compression) and support for bone graft. The goal of these devices is to stabilize the spine to facilitate bony fusion. However, typical cage-plates are formed of static components that are fraught with the complications associated with static plate fixation, namely graft stress shielding, graft overloading, subsidence, and graft failure. Graft stress shielding or graft overloading can lead to fibrous tissue formation or bone resorption, ultimately resulting in pseudarthrosis. For example, excessive strain on a bone graft and forming bone may lead to a fibrous non-union. As another example, inadequate strain on a bone graft and forming bone may facilitate primary bone formation and not facilitate secondary bone formation. Excessive micromotion may also lead to bone resorption and pseudarthrosis. Micromotion which exceeds 100 microns can lead to osteolysis and loss of osseointegration.
Total disc replacement is an alternative to arthrodesis for some patients with spinal degeneration. However, total disc replacement has different goals than arthrodesis and fusion. Total disc replacements attempt to return the disc to physiologic motion including flexion, extension, lateral bending, and torsion. Disc replacement devices are often structured to prohibit bony throughgrowth to facilitate long term motion preservation of the spinal motion segment
As a result, a need exists for devices and methods that utilize a bone graft and provide for the appropriate balance of facilitating load sharing while eliminating/reducing stress shielding and micro-motion to achieve vertebral arthrodesis and/or fusion.